1. Field of the Invention
The invention relates to a circuit arrangement for synchronizing an oscillator with an incoming synchronizing signal, comprising a phase discriminator having a first input terminal for receiving the synchronizing signal, a second input terminal for receiving a signal generated by the oscillator, and an output terminal for supplying a signal, which depends on the phase difference between the input signals of the phase discriminator, to a low-pass filter for smoothing the output signal of the phase discriminator and for applying a control signal to a control input terminal of the oscillator, the low-pass filter comprising at least a switch and a capacitor arranged in series therewith.
2. Description of Related Art
A circuit arrangement of this type is known from European Patent Application No. 72,751. The circuit arrangement described in this Application forms part of an integrated circuit which also incorporates the capacitor of the low-pass filter because the charge and discharge currents of the capacitor are very small, namely of the order of several tens nano-amperes, and because the switch conducts only during a part of the period for charging or discharging the capacitor. For this purpose the switch receives control pulses from the phase discriminator. However, the presence and the duration of these pulses depend on the phase difference established by the phase discriminator. Moreover, very small, stable currents can only be obtained when using certain integration techniques.